Effect Of MnO₂ Addition On The Structure And Properties Of (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ Ceramics At The MPB

Piezoelectric ceramics, as an advanced function ceramics, have been holding an important status in electronic ceramics domain. As for piezoelectric properties and actual application, polynary system piezoelectric ceramics based on PbTiO₃ and PbZrO₃ occupy dominion now. However, they contain 60～70% poisonous lead, which badly endanger human health and environmental protection. It is crucial that pollution of lead had blocked development of piezoelectric ceramics. So exploitation and study of lead-free piezoelectric ceramics have been becoming a hotspot home even all over the world.In the lead-free piezoelectric ceramics system, BNT-based piezoelectric ceramics are optimal candidates for practical application. BNT-based ceramics show large piezoelectric properties and some performances catch up with PZT-based ceramics. Therefore, the range of apparatus can be extended on the basis of properties of lead-free piezoelectric ceramics materials or we can improve the existent ceramics systems or exploit new ceramics systems on the basis of apparatus need. At present, replacement and doping by the conventional mixed oxide method are applied for improvement of BNT-based piezoelectric ceramics. It is dear that performances of BNBT near morphotropic phase boundary (MPB) at room temperature are the best, including piezoelectric strain constant (d₃₃) iS 125pC/N.In this paper, pure (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃ and (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃ with different amounts of MnO₂ modified, including 0wt%, 0.15wt%, 0.3%, 0.45%, were prepared by solid phase reaction, which is a conventional electronic ceramics preparation technology, based on existence condition of lab. The effect of MnO₂ addition and preparation technology on structure, dielectric properties and piezoelectric properties of (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃ ceramics were in detail studied. D/max-2550/pc x-ray diffraction instrument, which was made in Japan Rigaku company, and Quanta 200 scanning electron microscope, which was made in Holand philips-FEI company, were used to show and research on microstructures, surface-structure and change orderliness of ceramics. The densities of samples in different sintering temperature were tested by XT200A digital balance, which was made in Switzerland production. The dielectric properties and piezoelectric properties were measured by ZJ-4 quasi-static d₃₃ meter, which was made in china academy of sciences, and HP4294A impedance analyzer apparatus. Correlation of properties and microstructures were analyzed and discussed, and microstructures, dielectric properties and piezoelectric properties and so on were compared among (Bi_1/2Na_1/2)_0.94Ba_0.06 TiO₃ ceramics with different MnO₂ addition.According to the study of preparation technology, dielectric properties and piezoelectric properties of pure (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃, we find that densities, dielectric properties and piezoelectric properties appear optimal value at calcination 850℃and sintering 1160℃. So optimal sintering condition of pure (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃ is calcination 850℃and sintering 1160℃. By the study of MnO₂-doped (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃, results of experiments show that sintering temperature rapidly descend with Mn-doping increase, which suggest that MnO₂ reduce sintering temperature of (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃. X-ray diffraction patterns show that (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃ with MnO₂ addition samples all present pure perovskite structure and no secondly phase, which indicate that MnO₂ do not change microstructures of (Bi_1/2Na_1/2)_0.94Ba_0.06TiO₃. With MnO₂ adulterant addition, density of samples increase and density reach max 5.79g/cm³ when MnO₂ is 0.3wt%. However, density of samples descend for MnO₂＞0.3wt%. In addition, the experiment results also show that the dielectric constant, piezoelectric constant and electromechanical coupling factor of ceramics increase and then reduce with Mn-doping increase. These properties of ceramics obtain max valueε_r=879, d₃₃=160pC/N, k_p=28.46%, respectively, when MnO₂ is 0.3wt%. In the range of Mn-doping, the mechanical quality factor show reverse change trend. When MnO₂ ranges from 0wt% to 0.3wt%, the mechanical quality factor decrease evidently, and then increase for MnO₂＞0.3wt%, and attained min value 152.26 at MnO₂=0.3wt%. However, dielectric loss show different change trend with Mn-dopingo From 0wt% to 0.15wt%, dielectric loss increase, between 0.15Wt% and 0.3wt%, dielectric loss decrease, and then again ascended for MnO₂＞0.3wt%. The min value of dielectric loss is 0.026 at MnO₂=0.3wt%. In addition, large electromechanical coupling factor and electrical resistivity could be gained under low polar electric field when right MnO₂ were added, which indicate that proper MnO₂ effectively decrease coercive electric field.